Q: I've had a bad cold. Should I get out and exercise when I'm sick?

At what point are you too sick and at what point is it OK? I.E., Milton

Frustratingly enough, it all depends on whom you ask.

Some fitness gurus, like Dr. Joshua S. Fink, a physician and a personal trainer who runs training centers called Prescriptions for Fitness Inc. in Ridgefield, Conn., and Chappaqua, N.Y., said the simple answer is that if you're sick, don't exercise.

If you exercise while your viral infection is at its worst, which lasts from the 24 hours before onset of symptoms until three days later, "you decrease your immunity to fight a cold," he said. Immune cells called natural killer cells "decline if you exercise while you're ill with a cold," he said. Don't go back to training until you truly feel better, which is likely to take five to seven days. "There are 365 days in the year. Learn when to chill out rather than thinking, `No guts, no glory.' "

Once you resume training, he said, follow the "50 percent rule." Do half your usual exercise for half the usual time. Then gradually build up to normal.

Exercise physiologist Roger Fielding of the Sargent College of Health and Rehabilitative Sciences at Boston University took a slightly different view. You have to use your own judgment, he said, although you definitely should not exercise if you have a fever. If your cold symptoms are localized to your upper respiratory tract and you have no body aches, exercise if you feel like it. "I am nursing a cold right now," he said. "I ran yesterday outside and I am going to run today."

In a study several years ago published by the American College of Sports Medicine, researchers gathered 50 college students, divided them into two groups -- one that did supervised exercise and one that did not -- and then intentionally gave them all colds. There were no significant differences on a number of measures, including "mucus weight measurement" and symptom severity scores, the study found.

JUDY FOREMAN